SECTION Va.—Manufacture of cement and crucible steel.—. With pure ores and skillful puddling, it is possible to produce wrought-iron in which the phosphorus does not exceed .02 per cent. This pure iron may be converted into steel by placing it in fine charcoal and exposing it to a yellow heat. By a slow process, called cementation, the carbon penetrates the metal at the rate of about one-eighth inch every 24 hours, so that a bar five-eighths of an inch thick is saturated about 48 hours after it arrives at a proper temperature. Many tons of bars are treated at one time, and some arrive at a full heat much sooner than others, and remain longer at that temperature, so that it is necessary to break the bars after treatment and grade them by fracture. The point of saturation is about 1.50 per cent, of carbon, but the average will be about one per cent.
The steel thus produced is known as blister or cement steel. It contains seams and pits of slag which were in the wrought-iron, and these defects are of fatal moment in the manufacture of edged tools. To avoid this trouble, cement steel may be melted in crucibles, out of contact with the air,, and, being thus freed from the intermingled slag, can be cast into ingots. This double process is expensive, and a more common method is to put charcoal into the crucible with bar-iron, the absorption of carbon progressing with rapidity when the metal is fluid. This practice is almost universal in America, and it is claimed that it gives a steel equal in every respect to the older method, but against this it may be well to quote the following dictum of Seebohrn,* which expresses the ancient doctrines: "The best razor steel must be melted from evenly converted steel. It will not do to mix hard and soft steel together, or to melt it from pig let down' with iron, for it will not then possess the requisite amount of body, and the edge of the razor will not stand/'
* On the Manufacture of Crucible Cast-Steel, Journal I. and S. I., Vol. II. 1884, p. 372.